NEW YORK (Reuters Health) - Booster doses of hepatitis B vaccine up to 10 years after the original pre-adolescent vaccination prompt a robust hepatitis B virus surface antibody (anti-HBs) response in almost all recipients, Canadian researchers report in the October issue of Vaccine.

"Hepatitis B vaccines are commonly recognized as safe and efficacious in protection against infection," lead investigator Dr. Vladimir Gilca told Reuters Health. "However, uncertainties remain regarding the duration of protection. The results obtained 10 years after vaccinating... are very encouraging."

Dr. Gilca of Laval University, Quebec, and colleagues studied 559 subjects who had received 3 pediatric doses of Engerix-B (GlaxoSmithKline) when they were 8 to 10 years old. They went on to receive a booster dose 5 or 10 years later.

Anti-HBs was measured before and 1 month after primary vaccination, then 5 and 10 years later, before the booster dose as well as 1 month and 1 year post-booster.

After the booster at 5 years, 99% had detectable antibody levels and 96% had a fourfold or greater increase in anti-HBs. Anti-HBs geometric mean titers fell from 114,489 IU/L 1 month after the booster to 3354 IU/L 5 years later.

In the 10-year booster group, 96% had detectable anti HBs and 85% had a fourfold or greater increase. Geometric mean titers at 1 month post-booster were 31,030 IU/L.

The researchers point out that "if a booster is given there is flexibility to the timing of its administration." They intend to investigate response to a booster dose given at 15 years post-vaccination.

Dr. Gilca concluded, "Virtually all young adults show an excellent immune response to a challenge dose of vaccine, which means there is no need for booster doses for at least 10 years post-primary vaccination."